2004 == only one sensor, not separate sensors. That happened in '99 if I remember correctly which is when the BCM took over controlling the dash and talked with the PCM for its information instead of pulling directly from sending units & sensors. My '00 Bravada only had the one, two-wire sensor in the driver side head and just a blank, un-machined boss on the lower intake manifold where the 96-98 ETC sensor went.

The location for all 99+ is in the driver side cylinder head threaded into the head. The hole that it threads into opens up into the coolant passage in the cylinder head so expect to loose some coolant in the process. Have the new sensor ready to put in right away to minimize the lost coolant.

Just to clear up auto parts jargon, the sensor for the computer is the temperature sensor, the sensor for the gauge is the temperature switch. That will ensure you get the right thing when you ask the kid behind the counter. As for the later model single sensor... I dunno.. Temperature Sensor Switch?